I can drill it out, I've got the parts and bits to do it after buying them to remove a sheared mudguard bolt (screw extractor kit also has tap & die).
I don't own any mole grips, only pliers, will investigate getting some! Splitting the caliper isn't something I'd considered, thanks @kieranv
I don't own any mole grips, only pliers, will investigate getting some! Splitting the caliper isn't something I'd considered, thanks @kieranv